This removes:

* Python 3 variants (VARIANT:=python3)

* "for Python3" from package titles

* Package selection condition from package dependencies, e.g.
  +PACKAGE_python3-six:python3-light replaced with +python3-light

* "Default" package information sections, e.g.
  Package/python-six/Default removed and package details merged into
  Package/python3-six

* "(Variant for Python3)" from package descriptions

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This updates all Python packages that download their source from PyPi to
use pypi.mk.

This will allow future improvements/changes to pypi.mk to affect all
relevant packages.

This also makes it easier for future Python packages to start using
pypi.mk, when it's clear how it is used in existing packages.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

Signed-off-by: Karel Kočí <karel.koci@nic.cz>